Method and apparatus for pressurizing and depressurizing of fluids



1970 CHEN'YEN CHENG ETAL 3,489,159

METHOD AND APPARATUS FOR PRESSURIZING AND DEPRESSURIZING OF FLUIDS Filed Aug. 18, 1965 2 Sheets-Sheet 1 P V P V HIGH PRESSURE 2 2 i A a I PROCESSING VESSEL HIGH PRESSURE REJECT sow-nou- 1' a:

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CHEN-YEN CHENG BY SING-WANG CHEN? ATTORNEY Jan. 13, 1970 CHENYEN CHENG ET AL Filed Aug. 18, 1965 2 Sheets-Sheet 2 HIGH PRESSURE I I I v I I K PROCESSING 1 l I I FEED PRODUCT I STORAGE STORAGE I l I I DISPLACEMENT VESSEL PRODUCT I 8 I, 9 5 HIGH PRESSURE I PROCESSING I l I I I FEED PRODUCT STORAGE STORAGE i I ll DISPLACEMENT E D 6 VESSEL I PRODUCT FEED INVENTOR.

CHEN -YEN CHENG SING WANG CHENG ATTORNEY United States Patent 3,489,159 METHOD AND APPARATUS FOR PRESSURIZING AND DEPRESSURIZING OF FLUIDS Chen-Yen Cheng, Manhattan, Kans. (3555 E. Evans Ave., Denver, Colo. 80210), and Sin-Wang Cheng, 83, Chang An East Road, Section 1, Taipei, Taiwan Filed Aug. 18, 1965, Ser. No. 480,598

Int. Cl. F17d 1/18 U.S. Cl. 137-14 16 Claims ABSTRACT OF THE DISCLOSURE A method of and apparatus for effecting substantial energy cost reductions (especially in the processing of condensed-vapor or gas phase absentor largely condensed materials of fluid-like character) in connection with high pressure material processing techniques when fluids are supplied for subsequent introduction into a high pressure treating or processing zone at a relatively low pressure, and processed or treated fluids are to be subsequently discharged for further movement or storage at a low pressure.

Conventional energy conservation techniques entail extracting energy from fluids exiting from the high pressure treating zone by a turbine or the like and utilizing such extracted energy to drive a pump to 'force low pressure feed fluid into the high pressure treating zone. The inefliciencies of such conservation techniques and the high cost of apparatus used in the practice of such techniques are greatly reduced by effecting, according to the present invention, the introduction of feed fluid into and the removal of product fluid from the high pressure zone by exchanging flow work between the two fluids. The method involves isolation of a unit volume of 'feed fluid from a low pressure source thereof, pressurizing the unit volume of feed fluid by placing high pressure product fluid in pressure communication therewith in a displacement zone, and then displacing the unit volume of feed fluid from a low pressure source thereof, pressurizing the unit volume of feed fluid by placing high pressure product fluid in pressure communication therewith in a displacement zone, and then displacing the unit volume of feed fluid from the displacement zone into the process zone by moving product fluid from the process zone into the displacement zone. Subsequently the displacement zone is depressnrized, and the product fluid, now at low pressure, is displaced from the displacement zone by moving low pressure feed fluid into the displacement zone. The method also involves, when necessary, the introduction of feed fluid into the process zone at high pressure.

The apparatus involves a displacement vessel having a movable partitition therein separating the same into two portions, means is provided for alternately communicating the portions of the displacement zone with a feed fluid source and a product receiving zone on one hand and with the inlet and outlet of the process zone on the other hand. In the latter condition, a closed circuit or loop is defined, and a pump is provided to provide necessary circulation in the circuit. Means is also provided for introduction, when necessary, of fluid at high pressure into the pressure zone or vessel.

(I) INTRODUCTION A closed loop displacement technique is incorporated in the scheme of pressurizing a volume of a fluid and depressurizing an equivalent volume of another fluid so that flow work can be exchanged between them. Shaft work in the pump and in the turbine is reduced by the amount of the flow work exchanged, and mechanical work losses are correspondingly reduced.

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For a fluid system forming a closed loop, no flow work need be considered. A flow work exchanger uses a displacement vessel in which a feed and a product are alternatively admitted, pressurized and depressurized respectively by non-flow processes. Closed loop displacement operations are applied in pushing the 'feed into and discharging the product out of the processing system. The energy required is reduced to that of non-flow pressurization and depressurization plus some work required for circulation.

High pressure technology has been developed to the extent that many modern chemical processes are operated at high pressure levels. Such operations are adopted to those processes Where high pressures give favorable equilibrium (either physical or chemical). Most of the high pressure processes are, however, associated with systems which involve a gas phase because operating pressure influences the equilibrium of such a system to a greater extent. It was not until recently that large-scale high pressure processes were considered for development for a system composed entirely of condensed phases. It can be seen that, due to the small volume change involved in the transformation of a condensed system, a very high pressure is usually required to shift the equilibrium conditions any appreciable extent. The processes under development are: (i) a reverse osmosis process 1, 2, 3, 4) and (ii) a freezing process which achieves heat reuse by high pressure inversion of the order of melting points (5).

In a conventional continuous process, feed streams are pressurized and introduced into a processing system by high pressure pumps and the product streams are depressurized by activating turbine. The overall energy requirement (net work required) of the flow processes by way of conventional pressurization and depressurization is much larger than that of ideal reversible operations, mainly because of the multiplying mechanical inefficiencies involved in the pump and turbine. The cost of high pressure pumps and turbines is also high.

Mechanical work loss in a pump (or a turbine) is proportional to the magnitude of the shaft work. In the high pressure processing of a condensed system, the flow Work (PV) at the high pressure side contributes significantly to the shaft work. So, when flow work can be exchanged between a high pressure stream and a low pressure stream in a practical way, the magnitude of the shaft work will be greatly reduced and mechanical work losses will also be correspondingly reduced.

A practical way of exchanging flow work between equal volumes of two fluids is to use a flow work exchanger. This exchanger may be considered analogous to a heat exchanger. In a heat exchanger, one fluid is heated while another is cooled by an exchange of heat between them. In a flow work exchanger, one fluid is pressurized while another is depressurized through the use of a flow work exchange between them.

i. In a high pressure process, the volume of feeds to be pressurized is always greater than the volume of products to be depressurized. This is because, in order to have favorable equilibrium at a higher pressure, the volume of the system should shrink during the transformation. This difference between the volumes is called the excess volume of feeds. An excess feed volume, V is defined V =Sum of the volumes of feeds to be pressurized Sum of the volumes of high pressure products to be depressurized.

Since a flow work exchanger takes place between equal volumes of two fluids, the excess volume of feeds cannot receive flow work from product stream and has to be pressurized in a conventional way.

3 (n FLOW WORK EXCHANGER In the drawings:

FIG. 1-a is a subcombination of the apparatus of the invention,

FIG. 1b shows the processing vessel and displacement vessel,

FIG. 2 shows a first embodiment of the invention,

FIG. 3 shows a second embodiment of the invention,

FIG. 4 is a schematic of the invention applied to a reverse osmosis process, and

FIG. 5 is a schematic of the invention as applied to a freezing process.

The basic ideas which underlie the exchange of flow work can be explained in connection with FIGURES 1-a and 1-b. In FIGURE 1-a, flow work, p v is the work done on the unit mass of feed fluid as it is pushed past the entrance by the fluid behind it. Similarly, on passing the outlet, an amount of work, p v is done by the unit mass of fluid on the fluid just ahead of it (6). If a fluid system forms a closed loop as in FIGURE l-b and :he system is taken as the fluid within the closed loop, :here will be no flow work at all since all the fluid within the loop is considered part of the system and there is no surrounding fluid either to give or to receive flow work. in this way, a volume of feed is successfully pushed into :he processing system and an equivalent volume of a product is discharged from the processing system. This )peration will be referred to as a closed loop displacement mention in the following discussion. As shown in the igure, a pump M is used to circulate the fluids during his operation. Referring to FIGURES 1-b, 2 and 3, the )oundary of A and B fluids moves to the left within the lisplacement vessel during the closed loop displacement )peration.

A flow work exchanger incorporates such a closed loop iisplacement operation and some additional features, which will be described later, in the scheme of pressurizng a feed and depressurizing product. It can then draw low work from the volume of a high pressure product and, after some necessary upgrading, transfer it to an :qual volume of a feed.

The shaft work to be supplied for a reversible flow )rocess is Vd P1 p tl'ld the shaft work to be supplied for a reversible nonlow process is dV f p Due to the non-compressibility of the condensed system, he magnitude of the reversible flow process is much greater than that of the reversible non-flow process. The lifference between the two is the difference in the flow vorks, A(PV). So, if flow works can be exchanged be- .ween a product and a feed stream, the work to be sup- Jlied at the pump and the work to be recovered at the urbine are reduced to their non-flow values. In actual mention, some additional Work is required in the necesiary upgrading of flow work. It is, in fact, the work sup- )lied at a circulation pump to overcome irreversibilities vhich arise in the flow processes. Since the mechanical york loss in a pump or a turbine is proportional to its magnitude of shaft work, the adoption of a flow work :xchanger will result in the reduction of mechanical work osses in the pump and the turbine.

In order to incorporate the closed loop displacement :echnique in the scheme of pressurizing a feed and deiressurizing a product, the following problems have to :e overcome:

(1) Additional features should be added so that a Jolume of feed can be introduced and an equivalent volme of product can be discharged periodically.

(2) This operating fluids A and B have to be partitioned to prevent intermixing at their boundary in the displacement vessel.

(3) The boundary of the two operating fluids which has shifted during the closed loop displacement operation has to be restored periodically.

Pressurization of a feed and depressurization of a product in a high pressure processing imply a superposition of two operations. Pressurization of a feed means a non-flow pressurization and a displacement into the processing system. Depressurization of a product means a nonflow depressurization and a discharge out of the processing system.

A flow work exchanger should (i) take in a volume of a feed and discharge an equal volume of a product periodically, (ii) pressurize the feed taken in and depressurize the product to be discharged by non-flow processes and (iii) push the pressurized feed into and discharge the depressuriz/ed product out of the processing system by a closed loop displacement operation. In addition, these operations should be so arranged that the boundary of the operating fluids, A and B, restores its position periodically.

Before illustrating the actual operation of flow work exchangers, the solutions to the problems of partitioning two operating fluids during the closed loop displacement operation will be briefly outlined.

Any of the following can be used to partition the operating fluids.

(a) Use of a solid partition A solid partition, such as a circular disk, may be placed in the displacement vessel to separate the two fluids. Since the two fluids are at nearly the same pressure, no elaborate packing is required and no surface finishing is required on the inner surface of the vessel.

(b) Use of a displacement vessel of large L/D ratio Dispersion of fluids in a flow process is related to the length to diameter ratio (L/D) of the vessel and the flow rate. So, if a vessel of large L/D is used and the flow rate is kept low, dispersion of the fluids will be small and intermixing at the liquid boundary will be small. Intermixing at the boundary may be tolerated to a limited extent since it amounts to the mixing of a product with a feed and would not be detrimental in some applications such as sea water desalination. In practice, a bundle of small tubes may be used to serve as a displacement vessel. A more convenient way would be to insert parallel vanes within a large-diameter vessel. The vessel is then compartmentized and serves the same purpose.

(0) Use of a fluid which is immiscible with the operating fluids An immiscible fluid can be used to separate the two operating fluids under certain operating conditions. Large L/ D ratio of the displacement vessel, large interfacial tensions between the partition fluid and the operating fluids and low flow rate favor effective separation of the operating fluids.

(III) ILLUSTRATION OF A FLOW WORK EXCHANGER Flow work exchangers are classified according to the way of partitioning the operating fluids. The basic ideas and the functions to be performed by a flow work exchanger have already been outlined. This section considers how these basic ideas are embodied into a practical equipment to accomplish the required performances. The operational steps outlined here should be compared with the thermodynamic analysis.

FIGURES 2 and 3 show a flow work exchanger associated with high pressure processing. The flow work exchanger consists of a displacement vessel fitted with control valves, two low-head circulating pumps and a small capacity high pressure pump. In actual operation, several flow work exchangers may be installed and operated at the proper timing to give a more uniform flow of operating fluids.

(1) A flow work exchanger without a movable solid partition FIGURE 2 shows a flow work exchanger without a movable solid partition associated with high pressure processing. Assuming that the displacement vessel 1 is filled with a low pressure feed to start with, the operation proceeds in the following cyclic steps:

Step 1.With valves 2, 4, 5 and 6 closed and 3 open, some additional feed is pumped through pump 7 to pressurize the contents in the displacement vessel.

Step 2.With valves 2, 3, and 6 closed and valves 4 and 5 open, high pressure product fluid is admitted to the displacement vessel through valve 4 to displace the contents in the vessel. The pressurized feed is thus introduced into the processing system 8 through valve 5. Circulation pump 9 supplies the power required in this displacement operation. At the end of this operation, the high pressure product fluid fills the vessel.

Step 3.-With valves 2, 3, 4 and 5 closed, valve 6 is opened to depressurize the contents in the displacement vessel (i.e., the product fluid).

Step 4.With valves 3, 4 and 5 closed and valves 2 and 6 open, low pressure feed is admitted through valve 2 to displace the contents in the displacement vessel (viz. low pressure product) through valve 6. At the end of this operation, the displacement vessel 1 is filled with low pressure feed fluid, and the cyclic steps repeat.

The entire system is, therefore, divided into three zones. Fluids in zone I are under the high processing pressure, fluids in zone II are under the low pressure and the fluids in zone III are alternatively connected to the high and the low pressures. When a fluid partition is used to keep a feed fluid separated from the product fluid, the partition fluid is added at the inlet side of the displacement vessel at the start of steps 2 and 4. The partition fluid so introduced can be recovered.

(2) A flow work exchanger with a movable solid partition FIGURE 3 shows a flow work exchanger equipped with a movable solid partition, such as a circulator disk or a diaphragm. When the valves and pumps are labeled as shown, the operation steps closely follow those described in connection with a flow work exchanger without a movable solid partition.

A displacement vessel equipped with a solid partition should be distinguished from a pump equipped with a piston. In a pump, a movable piston is used to pressurize a fluid by a reciprocating motion. Thus, the piston is separating a fluid at two different pressures. Therefore, the cylinder of a pump should be well-finished, and elaborate packing is required to prevent fluid leakage across the piston. Since the solid partition in the displacement vessel of a flow work exchanger is separating two operating fluids at-nearly equal pressures, the solid partition can be very simply constructed and no finishing whatsoever of the vessel surface is required. A solid partition may be visualized as a rotor in a rotameter placed in a pipe of uni-form diameter.

What we claim as our invention and desire to secure by Letters Patent is as follows:

1. In apparatus for reducing pumping energy requirements in performing a high pressure process with respect to a fluid received and discharged at relatively low pressures, the improvement comprising a displacement vessel having a movable partition therein separating the interior thereof into first and second portions having pressure communication with each other through such partition, a high pressure process vessel having an inlet and an outlet, a feed conduit adapted to be connected to a source of a fluid to be processed in the process vessel, a discharge conduit adapted to be connected to a receiver of processed fluid, a first conduit means affording fluid communication between the first portion and the inlet of the process vessel and between said first portion and the feed conduit, said first conduit means being provided with a first valve means for selectively preventing fluid communication between said first portion and the feed conduit and between said first portion and the inlet of the process vessel, a second conduit means affording fluid communication between said second portion and the outlet of the process vessel and between said second portion and the discharge conduit, said second conduit means being provided with a second valve means for selectively preventing fluid communication between said second portion and the discharge conduit and between said second portion and the outlet of the process vessel, said displacement vessel, process vessel and the first and second conduit means constituting a fluid circuit when said first and second valve means prevent fluid communication between said portions and the feed and discharge conduits, a first pump means in said fluid circuit for causing fluid flow therein in such a direction that fluid flow in the first conduit means is from said first portion to the inlet of the process vessel and from the outlet of the process vessel to said second portion, whereby a path of fluid movement is defined that involves initial movement from the feed conduit into the first portion of the displacement vessel, thence from the first portion of the displacement vessel into the process vessel through the inlet of the process vessel, thence through the process vessel and into the second portion of the displacement vessel through the outlet of the process vessel, and finally from the second portion of the displacement vessel through the outlet of the process vessel, and finally from the second portion of the displacement vessel into the discharge conduit, the movements from the first portion of the displacement vessel into the process vessel and from the process vessel into the second portion of the displacement vessel being by way of separate first and second conduit means, and means for preventing any substantial fluid movement from the feed conduit to the discharge conduit by any path other than through the process vessel.

2. In apparatus for reducing pumping energy requirements in performing a high process with respect to a fl-uid received and discharged at relatively low pressures, the improvement comprising a displacement vessel having a movable partition therein separating the interior thereof into first and second portions having pressure communication with each other through such partition, a high pressure process vessel having an inlet and an outlet, a feed conduit adapted to be connected to a source of a fluid to be processed in the process vessel, a discharge conduit adapted to be connected to a receiver of processed fluid, a first conduit means affording fluid communication between the first portion and the inlet of the process vessel and between said first portion and the feed conduit, said first conduit means being provided with a first valve means for selectively preventing fluid communication between said first portion and the feed conduit and between said first portion and the inlet of the process vessel, a second conduit means affording fluid communication between said second portion and the outlet of the process vessel and between said second portion and the discharge conduit, said second conduit means being provided with a second valve means for selectively preventing fluid communication between said second portion and the discharge conduit and between said second portion and the outlet of the process vessel, said displacement vessel, process vessel and the first and second conduit means constituting a fluid circuit when said first and second valve means prevent fluid communication between said portions and the feed and discharge conduits, a first pump means in said fluid circuit for causing fluid flow therein in such a direction that fluid flow in the first conduit means is from said first portion to the inlet of the process vessel and from the outlet of the process vessel to said second portion, and means for maintaining the fluid pressure within the process vessel higher than the fluid pressure in the feed conduit.

3. The combination of claim 2, wherein the means for maintaining the fluid pressure in the process vessel higher than the fluid pressure in the feed conduit comprising means for introducing a fluid into the process vessel at a pressure greater than that prevailing in the feed conduit.

4. The combination of claim 2, wherein the means for maintaining the fluid pressure in the process vessel higher than the fluid pressure prevailing in the feed conduit comprises an auxiliary feed conduit adapted to be connected to a source of a fluid to be processed in the process vessel, said auxiliary feed conduit having fluid communication with the process vessel, and a second pump means in said auxiliary feed conduit for forcing a fluid therein into the process vessel at a pressure above that prevailing in the first mentioned feed conduit.

5. The combination of claim 4, wherein the auxiliary feed conduit affords fluid communication between the first mentioned feed conduit and the first conduit means.

6. The combination of claim 2, including means for positively preventing the movement of fluid from the feed conduit to the discharge conduit other than by way of the second conduit means.

7. A method for reducing pumping energy requirements in performing a high pressure process with respect to a fluid received and discharged at relatively low pressures, said method comprising a first step of concurrently communicating first and second portions of a fluid displacement zone respectively with a fluid feed source and a processed fluid receiver, a second step of concurrently communicating said first and second portions of the fluid displacement zone respectively with an inlet and an outlet of a process zone, a third step of continuously preventing commingling of fluids in the first and second portions of the displacement zone while continuously maintaining fluid pressure communication between fluids in such portions of the displacement zone, a fourth step of alternately performing one and discontinuing performance of the other of said first and said second steps, a fifth step of continuously maintaining the pressure in the process zone substantially higher than the pressure of the fluid feed source, and concurrently with the performance of said second step performing a sixth step of causing concurrent fluid flow from the outlet of the process zone to the second portion of the displacement zone and from the first portion of the displacement zone to the inlet of the process zone.

8. The method of claim 7, wherein the fifth step comprises establishing fluid communication between the process zone and a source of fluid maintained at a pressure in excess of the pressure prevailing in the fluid feed source.

9. The method of claim 8, including the seventh step of continuously preventing any substantial movement of fluid from the fluid feed source to the processed fluid receiver other than through the outlet of the process zone.

10. The method of claim 7, including the seventh step of continuously preventing any substantial movement of fluid from the fluid feed source to the processed fluid receiver other than through the outlet of the process zone.

11. In a method of relatively high pressure treatment of materials in a process zone and wherein a first fluid is supplied at relatively low source pressure, the pressure of the first fluid then being raised to the pressure prevailing in the process zone and then being moved into the process zone, and wherein a second fluid is moved from the process zone and then reduced in pressure to a discharge pressure slightly less than the source pressure, the improvement comprising moving a unit volume of the first fluid into a first portion of a displacement zone, then raising the pressure of such unit volume of the first fluid to the pressure prevailing in the process zone, then displacing such unit volume of the first fluid from the displacement zone and into the process zone by moving a unit volume of the second fluid into a second portion of the displacement zone, and then isolating the process zone from the displacement zone while reducing the pressure in the displacement zone to a pressure intermediate the source pressure of the first fluid and the discharge pressure of the second fluid.

12. The method of claim 11, including preventing the commingling of the first and second fluids in the displacement zone, and also preventing the first fluid from moving into contact with the second fluid except through the process zone.

13. The method of claim 11, wherein the unit volume of the first fluid is moved into the first portion of the displacement zone by the pressure differential between the low initial pressure of the first fluid and the discharge first portion of the displacement zone.

14. The method of claim 13, wherein the method is cyclically performed, and wherein the total volume of the first fluid introduced into the process zone per cycle must be greater than a unit volume in order to compensate for volume shrinkage occurring in the process zone and in order to maintain the pressure therein at the relatively high pressure, the additional step of intoducing into the process zone, during the course of each cycle and at the relatively high pressure, a volume of a feed fluid equal to the amount that said total volume exceeds a unit volume.

15. The method of claim 14, wherein the feed fluid introduced during said additional step has the same composition as the first fluid.

16. In a method of treating materials at a relatively high pressure in a high pressure zone, wherein a feed fluid is moved from a feed zone of relatively low pressure into the relatively high pressure zone, and wherein a product fluid is moved from the relatively high pressure zone to a product zone of relatively low pressure, the improvement comprising exchanging flow work between the product fluid and the feed fluid at substantially the pressure prevailing inthe high pressure zone by displacing product fluid from a second portion of a displacement zone into the product zone by flowing feed fluid into a first portion of the displacement zone at the relatively low pressure of the feed zone, while preventing fluid and fluid pressure communication between the high pressure zone and the displacement zone, thence preventing fluid and fluid pressure communication between the displacement zone and the feed and product zones, while displacing feed fluid from the first portion of the displacement zone into the high pressure zone by causing product fluid to flow from the high pressure zone into the second portion of the displacement zone at substantially the pressure prevailing in the high pressure zone, while continuously maintaining the contents of the high pressure zone at a pressure substantially greater than the fluid pressures in the feed and product zones.

References Cited UNITED STATES PATENTS 3,005,417 10/1961 Swaney 103241 X 3,090,325 5/1963 Ross 10324l X ALAN COHAN, Primary Examiner U.S. Cl. X.R. 

